Head through the first door, and cross the room. The blue key is in the first room to your right. Collecting the key will release a chaingunner, or a mancubus on HMP difficulty level or higher.

The blue key door can be found if you go out straight from the blue key room (that is, to the east) and follow the short corridor. It will be found on the right-hand side of the room. If you want to collect the box of shells before the door, walk behind the crates and climb up.

The rocket launcher should be in plain view - down the stairs from the blue door, on top of a pile of small crates.

To reach the red key, continue from the rocket launcher to head outside. There should be about three paths leading north; take the left most one (the one straight ahead from you), and take a left turn to the stairs which lead to the red key.

The route to the exit is located past the door east of the rocket launcher. Open this door with the red key, and head down the lift to the maze.

The quickest route through the maze is a simple left turn, with a gray metal wall with blue shiny things on it. Press "use" to lower the wall, revealing an arch-vile.

The exit switch is at the opposite of this final room, behind the monsters and two arachnotrons.

After the maze-like area behind the red door, you'll find a silver wall with blue lights on it that lowers as a lift. Instead of passing through to the other side, ride the lift back up. At the top is an alcove with a berserk pack. (sector 213)

Across from secret #1 is a second alcove with a security armor and a long secret pathway back to an earlier part of the level. (sector 214)

In the starting area, there is a brown-coloring on the gray wall. Open it to reveal a super shotgun. The super shotgun is on a lift that lowers to a watery tunnel containing monsters.

In the blue room south of the entrance, crossing to the southern end of the room lowers a platform with one or two barons of Hell. Collecting the supercharge on this lowered platform releases additional monsters.

In the blue key room, demons are not released if you do not attempt to collect the chainsaw or stimpacks.